1. Field of the Invention
The present invention relates to an ignition control device for an engine provided with a plurality of ignition plugs for each cylinder.
2. Description of the Related Art
Heretofore, there has been proposed an engine provided with two ignition plugs for each cylinder (refer to Patent Document 1 (Japanese Patent Laid-Open No. 4-112069)). In such an engine, when the engine runs at low speed, one ignition plug is ignited, and when the engine runs at high speed, two ignition plugs are simultaneously ignited to increase a combustion speed at each cylinder. As a result, combustion pressure is increased to thereby improve an engine output.
Unfortunately, in a case where one ignition plug is ignited when an engine runs at low speed, for example, the amount of non-combustion gas may increase. Thus, a secondary air supply device for supplying a part of intake air as secondary air to an exhaust pipe, or a fuel injection device that adjusts fuel injection quantity is operated to reduce the amount of non-combustion gas. However, such a device may not sufficiently clean up exhaust gas.
Furthermore, when an engine runs at high speed, a combustion speed of a gaseous mixture in a combustion chamber increases as an intake air speed increases. At the time, if two ignition plugs are simultaneously ignited, the combustion speed may be excessively increased to cause a noise such as a piston hammering sound to be increased.
Further, when an engine runs at high speed, a combustion speed of a gaseous mixture in a combustion chamber increases as an intake air speed increases. At the time. If two ignition plugs are simultaneously ignited, the combustion speed may be excessively increased to cause a noise such as a piston hammering sound to be increased. In addition, at the time, if two ignition plugs are simultaneously ignited, the combustion speed may be excessively increased to cause a noise such as a piston hammering sound to be increased.